Re: [PATCH] qemu-options.hx: Update descriptions of memory options for NUMA node

[Yohei Kojima]

ping


This patch updates an outdated description in qemu-options.hx .
The patch reflects the changes in qemu behavior already described in
another documentation, and it also changes paragraph structure for
further readability.

The original patch is:
https://patchew.org/QEMU/TYZPR06MB5418D6B0175A49E8E76988439D8E9@TYZPR06MB5418.apcprd06.prod.outlook.com/


On 2023/03/30 19:09, Yohei Kojima wrote:
> This commit adds the following description:
> 1. `memdev` option is recommended over `mem` option (see [1,2])
> 2. users must specify memory for all NUMA nodes (see [2])
> 
> This commit also separates descriptions for `mem` and `memdev` into two
> paragraphs. The old doc describes legacy `mem` option first, and it was
> a bit confusing.
> 
> Related documantations:
> [1] https://wiki.qemu.org/ChangeLog/5.1#Incompatible_changes
> [2] https://www.qemu.org/docs/master/about/removed-features.html
> 
> Signed-off-by: Yohei Kojima <y-koj@outlook.jp>
> ---
>  qemu-options.hx | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 59bdf67a2c..174f0d0c2d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -405,15 +405,22 @@ SRST
>          -numa node,nodeid=0 -numa node,nodeid=1 \
>          -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1
>  
> -    Legacy '\ ``mem``\ ' assigns a given RAM amount to a node (not supported
> -    for 5.1 and newer machine types). '\ ``memdev``\ ' assigns RAM from
> -    a given memory backend device to a node. If '\ ``mem``\ ' and
> -    '\ ``memdev``\ ' are omitted in all nodes, RAM is split equally between 
> them.
> -
> -
> -    '\ ``mem``\ ' and '\ ``memdev``\ ' are mutually exclusive.
> -    Furthermore, if one node uses '\ ``memdev``\ ', all of them have to
> -    use it.
> +    '\ ``memdev``\ ' option assigns RAM from a given memory backend
> +    device to a node. It is recommended to use '\ ``memdev``\ ' option
> +    over legacy '\ ``mem``\ ' option. This is because '\ ``memdev``\ '
> +    option provides better performance and more control over the
> +    backend's RAM (e.g. '\ ``prealloc``\ ' parameter of
> +    '\ ``-memory-backend-ram``\ ' allows memory preallocation).
> +
> +    For compatibility reasons, legacy '\ ``mem``\ ' option is
> +    supported in 5.0 and older machine types. Note that '\ ``mem``\ '
> +    and '\ ``memdev``\ ' are mutually exclusive. If one node uses
> +    '\ ``memdev``\ ', the rest nodes have to use '\ ``memdev``\ '
> +    option, and vice versa.
> +
> +    Users must specify memory for all NUMA nodes by '\ ``memdev``\ '
> +    (or legacy '\ ``mem``\ ' if available). In QEMU 5.2, the support
> +    for '\ ``-numa node``\ ' without memory specified was removed.
>  
>      '\ ``initiator``\ ' is an additional option that points to an
>      initiator NUMA node that has best performance (the lowest latency or